Diesel engine emissions have been an
ongoing environmental concern for the past few decades, and the United
States, Europe and Japan have responded to demands to reduce harmful
particulates and nitrogen oxides (NOx). In the U.S., particulate and NOx
levels were first regulated in 1988, with regulations becoming
increasingly stringent through the years. In fact, 1988 standards set NOx
and particulate levels at 14.4 g/kW-hr (grams/kilowatts – hour) and 0.8
g/kW-hr respectively, while 2010 standards have been set at 0.27 g/kW-hr
and 0.013 g/kW-hr respectively. By 2010, diesel engines will be considered
“clean,” but getting there will require sulfur-free fuel, improved
in-cylinder combustion, exhaust after-treatment, vehicle design changes
and diesel oils that are compatible with after-treatment systems.

Between the years 1988 and 1991,
emission standards were met by improving in-cylinder combustion through
the use of unit injectors, electronic controls, controlled air swirl,
improved combustion bowl design, reduced piston crevice volume,
turbo-charging, air inter-cooling and reductions in oil consumption.

The
year 1991 also saw the use of high top rings to lower particulate
emissions. By 1998, retarded fuel injection timing was introduced to meet
increasingly stringent NOx emission standards. High top rings and retarded
fuel injection timing increased soot loading on the oil, leading to the
introduction of API diesel oil category CH-4 in order to prevent viscosity
increases and increased wear due to soot.

In order to meet 2002 emission standards,
most engine manufacturers introduced exhaust gas recirculation (EGR)
engines, which recirculate a portion of the exhaust to the engine’s
combustion chamber, lowering peak combustion temperature. Although EGR
engines effectively reduce emissions, they also run hotter and introduce
higher levels of soot and acid into the oil, leading to increased wear,
increased oil viscosity and shorter oil drain intervals.

The API CI-4
diesel oil specification was introduced in December 2001 to protect against
the higher temperatures and increased levels of acids, soot and oxidation
associated with EGR engines, while some manufacturers released their own diesel
oil performance specifications in order to assure optimum protection for their equipment.
Mack released its stringent EO-N Premium Plus High Performance Diesel Engine Oil
specification in the spring of 2002, then upgraded it to EO-N Premium Plus
03 in April 2003 due to soot-related oil thickening and shear that
occurred after a certain length of highway time.

API issued an upgrade to
its CI-4 specification, CI-4 PLUS, in September 2004 in order to provide
improved oxidation resistance, shear stability, acid neutralization and
soot dispersancy for EGR engines. CI-4 PLUS certified diesel oils also
meet most of the individual manufacturer issued specifications and are
backward compatible with older diesel oil specifications and engines. CI-4
PLUS oils must first meet the original requirements of CI-4, with the
additional requirements of passing the 90-Pass Shear Stability Bench Test
and the Mack T-11 engine test, a more stringent upgrade of the Mack T-8E
soot-viscosity test required for CI-4.

In order to meet 2007 particulate
standards, exhaust after-treatment devices such as particulate filters (DPF’s)
and continuously regenerative traps (CRT’s) will be incorporated into
diesel engines, creating new challenges for diesel oils. AMSOIL Synthetic
Diesel Oils are ahead of the curve and ready to meet the challenges of
tomorrow.

Emission control technology has increased
soot loading of diesel oils, prompting original equipment manufacturers to
shorten drain interval recommendations. Even at increased soot levels,
AMSOIL Synthetic Diesel Oils continue to offer outstanding wear
protection. Soot and iron wear levels were measured over 900 hours of
operation in a 2002 EGR-equipped Mack LE613-Rear Loader running AMSOIL
15W-40 Synthetic Heavy Duty Diesel and Marine Motor Oil. As seen in the
graph, even at increased soot levels, the rate of engine wear remained
well below the Mack condemnation limit of 0.5 parts per million per hour
(ppm/h). (Amsoil Action News November 2005)

The Harmful Effects of Engine Soot

Engine soot is a common by product in internal combustion engines, formed as the result of
incomplete fuel combustion. Most fuels are composed of hydrocarbons, containing both carbon and
hydrogen, and when undergoing complete combustion, the only byproducts are carbon dioxide and water.
However, no engine is completely efficient and complete combustion does not occur. Complete combustion
would require a very lean ratio of fuel to air, whereas real engine conditions exhibit richer fuel mixtures.
The less air that is present in the ratio, the more favorable the conditions for soot accumulation.

Soot formation is more pronounced in diesel engines than gasoline engines due to the ways fuel is injected
and ignited. While fuel is injected during the intake stroke and ignited with a spark in
gasoline engines, it is injected during the compression stroke and ignited spontaneously from the pressure in diesel engines.
Combustion is more efficient in gasoline engines because the air and fuel have a chance to thoroughly mix,
while the late fuel injection in diesel engines produces fuel-dense pockets in the combustion chamber that produce soot
when ignited. Newer exhaust gas recirculation (EGR) diesel engines, designed to reduce NOx emissions by routing part of the
engine's exhaust stream through an intercooler and back to the intake manifold, further compound soot problems in diesel engine
oils.

Excessive soot formation in oil can be caused by a number of factors. Worn out rings or injectors, excessive idling, poor fuel
spray patterns and incorrect air-fuel ratios are major causes of soot formation. A faulty fuel nozzle may spray more fuel than
desired, increasing the fuel-to-air ratio and causing incomplete combustion and soot accumulation, or the air filter may become
clogged, decreasing air supply and increasing the fuel-air ratio.

Soot particles are spherical in shape and 98 percent carbon by weight. They are a very small size of around 0.03 microns, but they
often agglomerate to form larger particles. Although the majority of soot produced during combustion exits through the exhaust, some
passes through the rings of the combustion chamber and enters the engine oil. As long as these soot particles remain suspended in
the oil and are not allowed to agglomerate, they pose little risk to engine parts. It is up to the motor oil's
dispersants to keep soot particles dispersed. However, in high soot conditions, dispersants can become quickly depleted.

High soot load conditions lead to loss of oil dispersancy as an oil's dispersant additives are consumed. As dispersancy is lost, soot
particles agglomerate and form larger particles that build up on engine surfaces. This soot and sludge eventually impedes oil flow, and
it can also form on oil filters, blocking oil flow and allowing dirty oil into the engine. In addition, high soot levels within a
motor oil increase its viscosity, further impeding oil flow and increasing engine wear. Anti-wear additive
performance is also affected in high soot conditions as additives are gradually removed from the oil by adsorption to soot particles,
leading to increased wear and premature engine failure.

Another negative effect of high soot conditions is the formation of carbon particles on the piston ring grooves, causing degradation
of the oil seal between the ring and cylinder line and abrading the ring and liner. As the gap between the ring and liner increases,
combustion byproducts such as gases and unburned fuels blow into the crankcase, a
problem known as blow by, eventually causing expanding gases to lose ability to push the piston down and generate the power necessary
to propel the vehicle. Horsepower is lost and fuel efficiency decreases. Ring sticking and poor heat transfer from the piston to the
cylinder wall can also result.

AMSOIL synthetic diesel oils are formulated with robust additive packages
that effectively disperse soot particles so they do not agglomerate and
cause engine damage. In actual on-highway heavy-duty truck field trials,
at soot levels as high as 10 percent volume and higher, AMSOIL diesel oils
maintained an extremely low viscosity of 17 cSt. Excellent wear control
was maintained with an average iron content under 50 ppm. AMSOIL diesel
oils provide outstanding protection against viscosity thickening and soot
generated wear.